1. Field of the Invention
The present invention relates to a switched reluctance motor that is operated mainly in a specific rotational direction and is suitable for use as, for example, a power source for an electric vehicle.
2. Description of the Related Art
A typical switched reluctance motor (hereinafter referred to as "SR motor") has a ring-like stator having a plurality of pole portions that are disposed in a cylindrical arrangement and provided with coil windings, and a rotor rotatably disposed inside the stator and provided with projected poles that face the pole portions of the stator. The rotor is normally an iron core formed simply by stacking magnetic material plates such as iron or steel plates or the like. The coils and pole portions act as electromagnets to attract the projected poles of the rotor. The rotor continuously rotates by switching the coils to be energized synchronously with the rotation of the rotor.
This type of SR motor is disclosed in Japanese Patent Laid-Open No. Sho 48(1973)-77314, Japanese Patent Laid-Open No. Sho 61(1986)-203847 and U.S. Pat. No. 3,956,678.
The SR motor, which generates torque by exploiting magnetic attraction forces created between the magnetic poles of the rotor and the stator by energization of the coils, normally produces considerable vibrations during rotation. This is because in a cycle of energization, the magnetic attraction force in a radial direction increases with rotation of the rotor, reaches a maximum and abruptly discontinues at energization switching, so that vibrations in the radial direction are produced in both the rotor and the stator and propagate to other components.
The technology disclosed in U.S. Pat. No. 3,956,678 incorporates a plurality of slit zones formed on the sides of projected poles facing in a specific rotational direction of the rotor, in order to specify the rotational direction of the SR motor at the time of starting. Although this technology reduces the magnetic attraction force occurring at the time of energization switching, the technology also considerably reduces the torque output.